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Rainwater Collection Guide – Common Questions Answered

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In this article, we’ll answer some of the most common questions about rainwater collection, storage and use.

rainwater harvesting diagram

What is rainwater collection?

Rainwater collection and harvesting gathers rainwater and keeps it on site for later use.

This water can be used to provide water for landscaping and gardens, in-home use, wildlife, livestock, fire protection, stormwater management and rain gardens.

Harvesting rainwater is a great way to control run off, conserve water and reduce your water bill. Rainwater lacks chlorine and fluoride that is found in many municipal water supplies.

Why is there a Need for Rainwater Collection?

Unlike many well water and municipal water supplies, rain water is naturally soft. Normal, clean rain has a pH of between 5.0 and 5.5.

If you’re willing to invest in a system to use harvested rainwater for your household needs, you can enjoy cleaner clothes and people, longer appliance life and no hard water buildup on fixtures and pipes.

In your garden, rainwater is the best option for watering. It’s free of salts and other minerals that can build up in the soil and harm your plants.

Where groundwater is poor quality or unavailable, rainwater recovery may be your most affordable option for clean, safe water for you, your garden and livestock.

In urban and suburban areas, much of the surface area is made up of impenetrable surfaces. These include roofs, sidewalks, driveways, streets, etc.. Rainwater falls and is swept into storm sewers instead of slowly percolating into the soil.

Combine rainwater collection with landscaping options such as rain gardens, and you have better storm water management. We keep water on site longer and release it slowly into the soil. This is extremely helpful during heavy rains.

Municipal water also tends to be expensive, and many municipal water supplies are under stress. If you replace some of your water use with a rainwater catchment system, it reduces demand and saves you money.

rainwater collection system

Is it Illegal to Collect Rainwater?

Some states do have specific laws on the books limiting rainwater harvesting or use. It’s best to check with your local regulations before making a big investment.

States with rainwater collection regulations include:

  • Arizona
  • Arkansas
  • California
  • Colorado
  • Hawaii
  • Illinois
  • Nevada
  • New Jersey
  • North Carolina
  • Ohio
  • Oklahoma
  • Oregon
  • Rhode Island
  • Texas
  • Utah
  • Virginia
  • Washington
  • U. S. Virgin islands

You can learn more at State Rainwater Harvesting Laws and Regulations.

Can I Drink Rainwater?

In most cases, it is best to filter rainwater before using it for drinking water.

Gutters and downspouts collect leaves and other grime. The first water to come off the roof of your home when it rains has the most large debris, but rain drops form around dust. Even “clean” rainwater contains some dust particles.

For more information on potable water filtration see: Emergency Water Storage and Filtration – What you need to know before emergencies hit.

How much rainwater will I collect?

There are online rainwater harvesting calculators, but here are the basics.

One square foot covered with water an inch deep equals 0.6233 gallons. That means that the amount of water you could harvest from a 1000 square foot roof from 1 inch of rain is up to 623 gallons .

Due to splashing and other losses, the book “Rainwater Collection for the Mechanically Challenged” estimates that a more realistic number is 550 gallons of rainwater harvested per inch of rain per 1000 square feet of collection surface.

As you can see, a good rain can fill a water barrel pretty quickly, so make sure to include an overflow for your rainwater collection system.

Rainwater Storage Containers – Rain Barrels and Cisterns

A key component of your rain water collection system is storage. Some ways to store rainwater include:

  • Water barrels
  • Stone cisterns
  • Concrete or Ferro-Cement Cisterns
  • IBC Tanks
  • Metal Storage Tanks
  • Polypropylene Storage Tanks
  • Fiberglass Storage Tanks

In the book “Rainwater Collection for the Mechanically Challenged”, the authors recommend water barrels for small systems and fiberglass storage tanks for larger systems.

Stone cisterns are beautiful, but they can be difficult to maintain and cost prohibitive to build new.

Fiberglass cisterns are durable, UV resistant (which inhibits algae growth), and budget friendly. They can be painted with household latex paint to create a decorative rainwater cistern.

Water barrels are a great way to start with rainwater harvesting on a small scale. They are relatively inexpensive, especially if you can find the barrels cheap or free.

See Rain Barrels – DIY, Cheap, Decorative Options (Plus Care Tips) for how to build and care for a rain barrel.

For larger rainwater storage such as polypropylene or fiberglass tanks, check with farm supply or industrial supply stores.

rain barrels

Other Rainwater Collection and Storage options

Underground water tanks (also called cisterns) are an option. If they are installed wrong they and there is water in the soil, they can float up out of the ground creating a huge mess.

Underground tanks store between several hundred and 20,000+ gallons. They are expensive, ranging in price from around $1000 to over $10,000. In nearly all cases, they require permits and contractors to install.

If you want to learn more about how to design a rainwater harvesting system, plans for roof washing systems, and just about any other questions you may have on rainwater collection for household use, I recommend the book “Rainwater Collection for the Mechanically Challenged“. Another good reference is Essential Rainwater Harvesting.

Be Careful – Water is Heavy

Recently, I’ve seen a photo of a rainwater collection system featuring three 55 gallon plastic drums, stacked on their side, one above the other, in a wooden frame with PVC connections. I don’t recommend that rain barrel system, and I'll explain why.

Those plastic drums are heavy, and the PVC connections are hard piped. Once installed, it would be a bear to get in there and clean your barrels.

If you have full rain barrels, they could contain over 1200 pounds of water. I don't trust that the stand is sturdy enough to hold the barrels.

Many DIY designs use garbage cans to make a rain barrel. I don’t recommend that, because garbage cans are not built to stand around full of water, and chemicals may leach out of the plastic.

Sooner rather than later, that garbage can rain barrel will end up as garbage itself.

Do you Collect Rainwater?

Do you have rain barrels or another rainwater harvesting system? I’d love to learn more from those who use rainwater for household and livestock use.

So far we have 100 gallons of storage that we use seasonally, but I hope to add more moving forward.

More Gardening, Homesteading and Green Living Ideas

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